CONFIG_DEBUG_IMX27_UART is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

i.MX27 Debug UART

configname: CONFIG_DEBUG_IMX27_UART

Kernel low-level debugging port
└─>i.MX27 Debug UART
In linux kernel since version 5.2 (release Date: 2019-07-07)  
Say Y here if you want kernel low-level debugging support
on i.MX27.